Patent application title: MICRODISPENSING PUMP

Abstract:

Various pump features are provided. In a first aspect, a pump is provided
having an actuator with a nozzle and a releasable cap having a first
shield located to entrap a fixed volume of air about the nozzle. In a
second aspect, a valve seat is located along a pump's internal fluid
passage with deflectable spring arms extending therefrom that
are-deflectable in response to movement of a check valve element. In a
third aspect, a compliant shut-off valve feature is provided, wherein, a
first end of a tubular piston is deflectable in response to interferingly
engaging the head of the poppet. In a fourth aspect, a pump includes a
pump inlet, and a reservoir having a first portion and a second well
portion in open fluid communication. Fluid may be trapped within the well
portion at various angular orientations of the pump.

Claims:

1. A pump comprising:a pump inlet; anda reservoir having a first portion
and a second well portion, said first portion and said well portion being
in open fluid communication, said well portion encompassing less volume
than said first portion, wherein said pump inlet being locatable in said
well portion.

2. A pump as in claim 1, wherein said well portion is located
gravitationally below said first portion.

3. A pump as in claim 1, wherein said volume of said well portion being
greater than one dose of the pump.

4. A pump as in claim 1, wherein said well portion is generally
cylindrical.

5. A pump as in claim 1, wherein said well portion is concave.

6. A pump as in claim 1 further comprising a dip tube, wherein said pump
inlet is formed at an end of said dip tube, said dip tube being
extendable into said well portion.

7. A pump comprising:an actuator having a nozzle; anda releasable cap for
selectively covering said actuator, said releasable cap including a first
shield located to at least partially cover said nozzle with said cap
covering said actuator, said first shield entrapping a fixed volume of
air about said nozzle when at least partially covering said nozzle.

8. A pump as in claim 7, wherein said releasable cap further includes a
second shield located spaced-apart from said first shield.

9. A pump as in claim 8, wherein said first and second shields are located
diametrically opposite on said cap.

10. A pump as in claim 7, wherein said releasable cap is formed to
releasably engage a portion of the pump surrounding said actuator.

11. A pump as in claim 7, wherein said first shield includes an inner
surface being at least partially flat.

12. A pump as in claim 11 further comprising an annular rim located about
said nozzle, said inner surface of said first shield being formed to
abut, or near abut, said rim with said first shield at least partially
covering said nozzle.

13. A pump comprising:a tubular piston having first and second ends; anda
poppet having an enlarged head, said head having a diameter greater than
the diameter of said first end of said piston, said first end of said
piston being deflectable in response to interferingly engaging said head
so as to define a seal therewith.

14. A pump as in claim 13, wherein said piston having an inner surface,
said inner surface of said piston on, or in proximity to, said first end
interferingly engaging said head.

15. A pump as in claim 13, wherein said first end of said piston is formed
with a wall thickness less than that of adjacent portions.

16. A pump as in claim 13, wherein said head includes a first arcuate
portion, said first end of said piston interferingly engaging said first
arcuate portion.

17. A pump as in claim 16, wherein said head includes a second arcuate
portion extending from said first arcuate portion.

18. A pump as in claim 13, wherein said piston further includes a shoulder
for engaging a portion of the pump and for limiting the extent of
movement of said piston, said shoulder being spaced from said first end
of said piston.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

[0001]This application is a continuation of U.S. application Ser. No.
10/123,390, filed Apr. 16, 2002, now allowed, which claims priority of
U.S. Provisional Application No. 60/284,157, filed Apr. 16, 2001, the
entire contents of both cases being incorporated by reference herein.

BACKGROUND OF THE INVENTION

[0002]Microdispensing pumps are known in the prior art, such as those
disclosed in U.S. Pat. No. 5,052,435, which issued Oct. 6, 1992; U.S.
Pat. No. 5,881,956, which issued Mar. 16, 1999; and WIPO Published Patent
Application No. WO 01/14245. The disclosures of these references are
incorporated by reference herein in their respective entireties.

[0003]Although microdispensing pumps are known in the prior art, because
of the minute doses of the pumps (5-15 microliters), microdispensing
pumps have problems associated therewith not found with pumps used for
larger dosages. For example, fluid residing within, or adjacent to, a
nozzle may evaporate between doses, thereby altering the volume of a
next-administered dose. With relatively large doses, typically in the
range of 80-100 microliters, evaporation of such fluid is generally
inconsequential in maintaining required dosage amounts. However, such
evaporation may have an effect on microdoses.

[0005]The problems noted above are addressed with a microdispensing pump
formed in accordance with the subject invention. Different features of a
microdispensing pump are described herein which may be used in various
combinations, or each singularly, and also may be used in various pump
applications, not limited to microdispensing pumps.

[0006]In a first aspect of the subject invention, an evaporation-reduction
feature is provided, wherein a microdispensing pump having an actuator
with a nozzle is provided with a releasable cap for selectively covering
the actuator. The releaseable cap includes at least a first shield
located to at least partially cover the nozzle with the cap covering the
actuator such that the first shield entraps a fixed volume of air about
the nozzle when at least partially covering the nozzle. Preferably, an
annular rim extends about the nozzle formed to abut, or near abut, the
front shield to cooperatively entrap the fixed volume of air. In this
manner, evaporation of fluid from the nozzle is minimized, and ideally
avoided. In a further preferred embodiment, a second shield may be formed
on the cap for covering an accessway to the actuator necessary for
operation of the pump.

[0007]In a second aspect of the subject invention, a check valve element
return feature is provided, wherein a valve seat is located along the
pump's internal fluid passage with a plurality of deflectable spring arms
extending from the valve seat. A valve element, e.g., a ball check valve
element, is disposed between the spring arms and the valve seat, with the
spring arms being deflectable in response to movement of the check valve
element away from the valve seat. Preferably, the spring arms urge the
check valve element into sealing engagement with the valve seat. Upon
sufficient fluid pressure, the check valve element is lifted from the
valve seat causing deflection of the spring arms. Memory of the spring
arms causes the check valve element to return to the valve seat and form
a seal therewith.

[0008]In a third aspect of the subject invention, a compliant shut-off
valve feature is provided, wherein, in one embodiment, a tubular piston
is disposed about a poppet having an enlarged head formed at one end
thereof. The head has a diameter greater than the diameter of a first end
of the piston, and the first end of the piston is deflectable in response
to interferingly engaging the head. As such, the first end of the piston
is able to form a seal with the head upon engagement therewith. The seal
is defined over a range of movement of the piston relative to the head.
In this manner, sealing of the compliant shut-off valve is unrelated to
limiting the upward travel of the piston.

[0009]In a fourth aspect of the subject invention, a fluid trapping well
is provided, wherein a microdispensing pump includes a pump inlet, for
example, at the end of a dip tube, and a reservoir having a first portion
and a second well portion in open fluid communication. The well portion
encompasses less volume than the first portion and is positioned such
that the pump inlet is locatable in the well portion. In this manner,
fluid may be trapped within the well portion at various angular
orientations of the pump to communicate directly with the pump inlet.
Because of the reduced volume of the well portion relative to the
remainder of the reservoir, fluid may be maintained in communication with
the pump inlet for a longer duration over various orientations of the
pump, as compared to a typical cup-shaped reservoir used in the prior
art. Such fluid being encouraged to reside in the well portion through
capillary attraction between the fluid, the dip tube, and the well
portion.

[0010]These and other features of the invention will be better understood
through a study of the following detailed description and accompanying
drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a perspective view of a pump formed in accordance with one
or more aspects of the subject invention;

[0012]FIG. 2 is similar to FIG. 1 with the releasable cap in an open
position;

[0013]FIG. 3 is a schematic cross-sectional view with the releasable cap
in a closed position;

[0014]FIG. 4 is a cross-sectional view of the releasable cap taken along
line 4-4 of FIG. 5;

[0015]FIG. 5 is a bottom plan view of the releasable cap;

[0016]FIG. 6 is a schematic of a check valve element disposed between
spring arms and a valve seat in accordance with a check valve element
return aspect of the subject invention;

[0017]FIG. 7 is a top plan view of a possible arrangement of the spring
arms and the check valve element;

[0018]FIG. 8 is a schematic with the check valve element separated from
the valve seat and the compliant shut-off valve open;

[0019]FIG. 9 is a partial cross-sectional view of a compliant shut-off
valve aspect of the subject invention;

[0020]FIG. 10 is a top plan view of the arrangement of FIG. 9; and,

[0021]FIGS. 11-14 are schematics of different embodiments of a
fluid-trapping device aspect of the subject invention.

DETAILED DESCRIPTION OF THE INVENTION

[0022]Various features of the pump are described herein which may be used
singularly or in various combinations. These features can be used with
known pump features, although the features are particularly well-suited
for use in microdispensing pumps. To illustrate the various aspects of
the subject invention, a representative pump and representative pump
features are described herein and depicted in the drawings. It is to be
understood that the particular pump and pump features are described and
depicted for illustrative purposes only, and any pump configuration (and
any configuration of pump features) may be used consistent with the
principles described herein.

[0023]With reference to FIGS. 1 and 2, a pump 10 is depicted for
dispensing fluid, particularly ophthalmic fluid medication. The pump 10
generally includes a handle 12, a neck portion 14, an actuator 16
disposed within the neck portion 14 and a flip cap 18 hingedly mounted to
the neck portion 14 via a hinge 20. A nozzle 21 is formed in the actuator
16 to dispense the fluid upon actuation of the dispenser; the actuation
preferably being achieved by depressing the actuator 16 and causing
downward travel thereof. The dispenser may be of a lift-pump type formed
in accordance with the teachings set forth in U.S. Pat. No. 5,881,956; of
a compression-pump type; or of any other type known to those skilled in
the art. For clarity, the various aspects of the subject invention are
discussed in turn, but are to be understood that these features may be
used one or more in combination, or each singularly.

Evaporation-Reduction Feature

[0024]With reference to FIGS. 1-5, the hinge 20 is of any type known to
those skilled in the art, including being integrally formed with the neck
portion 14 and the flip cap 18. It is preferred that the cap 18
releasably engage the neck portion 14 to maintain a closed state with the
pump 10 not being in use. To this end, a catch 22 may be provided which
is inwardly deflectable to engage and bear against an inner surface of
the neck portion 14 in a closed state, as shown in dashed lines in FIG.
4. The catch 22 is preferably located opposite the hinge 20. To
facilitate release of the cap 18 from the neck portion 14, a notch 24 may
be formed extending from an upper edge of the neck portion 14 such that a
portion of a lower surface of the cap 18 is exposed in a closed state.
This arrangement allows for force to be applied against the exposed
portion of the cap 18 to lift the cap 18 up from the neck portion 14,
thus releasing it from the neck portion 14. Optionally, a tab 25 may
extend from the cap 18, as shown in dashed lines in FIG. 5, against which
a user's finger may press to open the cap 18.

[0025]In a preferred embodiment, the hinge 20 has memory so that it
springs open the cap 18 upon the cap 18 being separated from the neck
portion 14. As will be appreciated by those skilled in the art, the catch
22 should have sufficient holding strength to overcome the memory of the
hinge 20 when the cap 18 is closed. Alternatively, the hinge 20 can be
formed as a true living hinge, without any memory.

[0026]As best shown in FIG. 2, the flip cap 18 is formed with two
depending shield portions 26 and 28 which are preferably located
diametrically opposite about the cap 18. The front shield portion 26 and
the rear shield portion 28 need not be of equal length. Correspondingly,
arcuate recesses 30 and 32 are formed in the neck portion 14 dimensioned
to register with the shield portions 26 and 28, respectively. The front
recess 30 is formed with sufficient depth to ensure that the nozzle 21 is
exposed during a dispensing procedure, including taking into account any
downward descent of the nozzle 21 upon actuation. The rear recess 32 is
relatively shallow, yet provides an accessway to the actuator 16 to allow
the finger of the user to move (e.g., depress) the actuator 16 without
interference of the neck portion 14 during actuation. The length of the
rear recess 32 is a function of the extent the actuator 16 must travel
downwardly in dispensing fluid; in turn, downward travel of the actuator
16 is typically a function of a pump's piston stroke--a relatively short
piston stroke will require a relatively short rear recess 32.
Advantageously, the shield portions 26, 28 provide the pump 10 with an
aesthetically-pleasing appearance, which is further enhanced by forming
the cap 18 of transparent material. Transparent material adds to both the
appearance and facilitates a user's ability to orient the pump 10
correctly before opening it (i.e., releasing the cap 18). The cap 18 may
be formed of polypropylene.

[0027]The shield portions 26, 28 have arcuate outer surfaces 34, 36,
respectively, which may be formed with the same degree of curvature as
the neck portion 14 so as to define the appearance of the continuous
cylinder (FIG. 1) with the cap 18 in a closed position. Preferably, the
edges of the shield portions 26, 28 overlap, at least in part, the edges
of the recesses 30, 32 to block the ingress of contaminants into the neck
portion 14. For example, the edges of shield portions 26, 28 and the
recesses 30, 32 may be cooperatively tapered, as shown in FIG. 3. The
overlapping edges also properly locate the cap 18 relative to the neck
portion 14, minimizing "free play" therebetween.

[0028]With reference to FIGS. 3-5, as an additional feature, a flat
surface 38 (hatched in FIG. 4 for clarity) may be formed across an inner
surface 40 of the front shield portion 26. As shown in FIG. 3, the flat
surface 38 is formed to abut, or near abut, an annular front outer rim 42
of the nozzle 21, thereby entrapping a body of air which occupies void 44
about any fluid meniscus M of fluid remaining in the nozzle 21. Generally
the meniscus M will come to rest, after a dispensing procedure, either
level with a mouth 19 of the nozzle 21, or in proximity thereto. The
mouth of the nozzle 21 is located at the center of a conical protrusion
46 projecting from an inner part of the nozzle 21.

[0029]The void 44 exists to provide space for any excess fluid to run away
from the mouth 19 of the nozzle 21, thereby allowing the nozzle 21 to
remain clean. In effect, the flat surface 38 acts as a lid on the void 44
to trap a body of air. The small entrapped body of air limits the
evaporation of the fluid from the nozzle 21. In particular, the ability
of the entrapped body of air to accommodate humidity, which causes
evaporation of the fluid, is limited. A point is reached where the
entrapped air becomes saturated and evaporation ceases. More generally,
the shields 26, 28 restrict moisture into the neck portion 14 through the
recesses 30, 32, which are necessary for proper operation of the pump 10
(i.e., exposure of the nozzle 21; and accessway to the actuator 16).

[0030]It has been found that leaving the nozzle 21 exposed to ambient air,
without any attempt to control the volume of air available to nozzle 21,
results in much greater evaporation from the nozzle 21 than with the
inventive arrangement described herein. Controlling evaporation is
critical to ensuring that a first dose administered by the pump 10 after
a period of rest is not deficient due to the evaporation effects at the
nozzle 21. With the use of the shields 26, 28, air flow into the neck
portion 14 below the cap 18 and about the actuator 16, is limited. The
use of the flat surface 38 enhances the ability to restrict air flow to
the nozzle 21.

Check Valve Element Return Feature

[0031]With reference to FIGS. 6-8, a check valve element return aspect of
the subject invention is depicted which may be used in various pump
structures, both in an inlet check valve application or as an outlet
check valve application. The check valve element return arrangement can
be placed along any location in a fluid pathway of a pump. To illustrate
this aspect of the subject invention, reference is made to FIGS. 6-8,
wherein a fluid passage 56 is defined to extend from a tubular piston 48
into the actuator 16. The flow of fluid passing through the fluid passage
56 is regulated by a check valve element 58, which is preferably a ball
check valve element. A valve seat 60 is defined to cooperate with the
check valve element 58 and to form a seal therewith.

[0032]A plurality of deflectable spring arms 62 extends from the valve
seat 60 to limit the travel of the check valve element 58 away from the
valve seat 60. Preferably, three of the spring arms 62 are provided, and
more preferably, the spring arms 62 are equally spaced about the valve
seat 60 (e.g., with three of the spring arms 62, the spring arms 62 would
be spaced 120° apart). The spring arms 62 are cantilevered to the
valve seat 60 so as to be outwardly deflectable upon upward movement of
the check valve element 58. Spring arms 62 are formed with sufficient
stiffness to limit the travel of the check valve element 58. In addition,
the deflection of the spring arms 62 generates return spring force which
urges the check valve element 58 to return to the valve seat 60. It is
preferred that the spring arms 62 be formed of polypropylene. It is
preferred that the spring arms 62 be in continuous contiguous contact
with the check valve element 58.

[0033]The spring arms 62 are shown to have a general hook shape. The
spring arms 62 may be formed with any shape wherein portions of the
spring arms 62 are located above the check valve element 58 so as to
restrict movement thereof away from the valve seat 60 as described below
(e.g., the spring arms 62 may be slanted plank-shaped members). The
spring arms 62 are preferably identically or substantially identically
formed.

[0034]Upon actuation of the pump 10, fluid is pressurized and forces the
check valve element 58 to separate from the valve seat 60, thereby
allowing the fluid to continue traveling through the fluid passage 56.
The check valve element 58 presses against the spring arms 62 and, under
internal pressure of the fluid, moves away from the valve seat 60 and
causes deflection of the spring arms 62 (FIG. 8). As the fluid travels
past the check valve element 58, internal pressure of the fluid decays
and eventually the return spring force of the spring arms 62 urges the
check valve element 58 towards the valve seat 60, and preferably into
contact with the valve seat 60 so as to form a seal therewith. The spring
arms 62 are formed with inherent memory which tends to return the spring
arms 62 to their original positions.

[0035]Advantageously, the spring arms 62 provide a centralizing effect in
urging the check valve element 58 into contact with the valve seat 60. In
particular, the extent each of the spring arms 62 is deflected is
proportional to the amount of return spring force provided by each of the
respective spring arms 62. For example, with reference to FIG. 7, if the
check valve element 58 drifts toward one of the spring arms 62 and causes
more deflection thereof as compared to the other spring arms 62, that
spring arm 62 will provide a greater spring return force than the other
spring arms 62, as designated by the arrow. The additional return spring
force will compensate for the drift. With the other spring arms 62 also
providing return spring force, the spring arms 62 collectively cause the
check valve element 58 to be centralized relative to the valve seat 60.
To further enhance the centralizing effect, the spring arms 62 are
preferably each formed with an enlarged free end 66 with the enlarged
portion extending inwardly (FIG. 6).

[0036]In a preferred arrangement, free ends of the spring arms 62 define a
locus of spaced-apart points, A, B, C, which define an area smaller than
the diameter of the check valve element 58. In this manner, passage of
the check valve element 58 through the spring arms 62 is restricted.

Compliant Shut-Off Valve Feature

[0037]With respect to a third aspect of the subject invention, a shut-off
valve feature is provided which operates over a range of positions of a
pump's piston, thereby separating control of the end of stroke of the
piston from control of sealing a fluid passage. Separating control in
this way allows piston upward travel to be controlled at a lower point on
the piston, and, therefore, is subject to reduced manufacturing tolerance
variations bringing improved accuracy.

[0038]To illustrate this aspect of the invention, reference is made to
FIGS. 6, 9 and 10. Although a specific structure of a poppet and piston
are depicted and described herein, any structural arrangement may be used
which is consistent with the principles herein.

[0039]FIG. 9 is an enlarged view of a head 54 of a poppet 50, also shown
in FIG. 6. Preferably, the head 54 is formed with a large arcuate portion
68 and a smaller arcuate portion 70, with the radius of the large portion
68 being greater than the radius of the small hemispherical portion 70.
For reduction of fluid drag, the smaller arcuate portion 70 is preferably
hemispherical (i.e., generated about a single radius).

[0040]The tubular piston 48 is formed with a deflectable, annular collar
72 at one end thereof, preferably having a wall thickness less than that
of adjacent portions. The collar 72 has a smaller diameter than the head
54 (particularly the arcuate portion 68) and is dimensioned for an
interference fit about the head 54 (thereby resulting in the outward
deflection of the collar 72), as shown in FIGS. 9 and 10. It is preferred
that inner surface 71 of the piston 48 on, or in proximity to, the collar
72 interferingly engage the head 54.

[0041]The piston 48 is shown to be disposed about a portion of the poppet
50. Beneficially, the piston 48 provides a centralizing effect to the
head 54.

[0042]Upon the piston 48 translating the furthest upward extent of its
stroke, the collar 72 engages the head 54 and deflects about it. The
piston 48 may be urged by a biasing device (not shown) upwardly and into
engagement with the head 54. The deflection of the collar 72 causes a
hoop stress to be generated in the collar 72, resulting in tight
engagement of the collar 72 with the head 54. Advantageously, the tight
engagement of the collar 72 about the head 54 is over a length of sliding
movement of the piston 48 with a seal being formed at any point over a
range of positions R--the defined seal acts as a shut-off valve which
stops the flow of fluid about the head 54. As shown in FIG. 8, upon a
downward stroke of the piston 48, the collar 72 disengages from the head
54, thereby allowing fluid to flow past the head 54.

[0043]With reference to FIG. 6, the upward stroke of the piston 48 is
limited by the interengagement of at least one shoulder 74 formed on the
piston 48, and at least one stop 76 formed on a portion of the pump 10.
The upward movement of the piston 48 is provided by a biasing device
(e.g., a coil spring) which is not shown. In the configuration shown in
the drawings, the piston 48 is fixed (e.g., by an interference fit) to a
valve housing 78, which, in turn, is fixed to the actuator 16.
Accordingly, the piston 48, the valve housing 78, and the actuator 16
move in unison. The piston 48 is urged downwardly by depression of the
actuator 16.

[0044]By spacing the collar 72 from the shoulder 74, advantageously, the
limit on the upward stroke of the piston 48 is separately established
from the shut-off valve, and is thereby controlled over a shorter
distance relative to the downward stroke of the piston 48. Controlling
the piston stroke over this shorter distance enables the individual
components which cooperate to effect the upward and downward limits of
travel of the piston to be manufactured to tighten limits, and therefore,
a smaller variation in dose accuracy is maintained. With the subject
invention, the collar 72 allows the shut-off valve to be defined over a
range of piston movement, thus, reducing reliance on manufacturing within
tolerances.

[0045]To allow for proper operation of the pump 10, the collar 72 should
be formed sufficiently resilient to repeatedly engage the head 54
interferingly without losing the ability to form a seal with the head 54.
To this end, the collar 72 may be formed of polyethylene, while the head
is formed of polypropylene.

Fluid Trapping Device

[0046]In a fourth aspect of the subject invention, it is desired to
maximize the ability to maintain fluid stored in a reservoir in fluid
communication with an inlet of the pump. Particularly, with the pump 10
dispensing microdoses (5-15 microliters), it is desired to maintain a
constant supply of fluid to the pump to minimize the ingress of air into
the pump, especially after priming. With microdoses, air bubbles may not
only disrupt the dosage volume, but even cause stalling.

[0047]With reference to FIGS. 11-14, the pump 10 is formed with a
reservoir 80 that contains fluid F. The fluid F may be drawn via a dip
tube 82 or other structural element having a fluid inlet 84. With the
pump 10 being in a vertical position (relative to gravitational
orientation) as shown in FIG. 11, the fluid inlet 84 of the dip tube 82
is locatable within the fluid F. To ensure the fluid inlet 84 is
continuously submerged, the reservoir 80 is formed with a first portion
85 and a second well portion 86 in open fluid communication. The well
portion 86 is preferably located gravitationally below the first portion
85 and encompasses less volume than the first portion 85. As shown in
FIG. 12, the dip tube 82 is extendable into the well portion 86, wherein
the well portion 86 retains the fluid F with the pump 10 being in a
non-vertical position, including a fully horizontal position.
Specifically, the depth of the well portion 86, as well as, the capillary
attraction between the fluid F, the dip tube 82, and the well portion 86,
will coact to retain the fluid F in various angular orientations of the
pump 10. In addition, it is preferred that the well portion 86 be sized
to retain at least one dose, more preferably at least five doses, of the
fluid F to reduce the possibility of drawing air into the pump 10.

[0048]The well portion 86 acts to temporarily retain the fluid F and is
not a permanent reservoir. In addition, the well portion 86 cannot
compensate for all angular orientations of the dispenser 10, especially
where the dispenser 10 is inverted with the reservoir 80 being at least
partially located gravitationally above the nozzle 21.

[0049]It is preferred that the fluid inlet 84 of the dip tube 82 be
beveled and oriented away from the nozzle 21 so as to encourage any air
bubbles that are evacuated from the dip tube 82 during initial priming to
break away cleanly from the dip tube 82 and not adhere onto the fluid
inlet 84 of the dip tube 82.

[0050]FIGS. 11 and 12 depict the well portion 86 as cylindrical. Other
forms are possible. For example, FIGS. 13 and 14 show a second embodiment
of the reservoir 80, wherein the well portion 86 is concave.

[0051]Various changes and modifications can be made to the present
invention. It is intended that all such changes and modifications come
within the scope of the invention as set forth in the following claims.